I have a licence question. I’m going to buy some sounds for my future projects, so that I don’t have the watermark in my videohive preview. But I have several animations for one sound (still selling as one item so it is one video), do I have to buy one licence for each time you hear the sound in the preview or is one licence enough to use it as often as I want in one video?

I would say it’s more logical to say one video = one licence but I better make sure

Because the video is a “single application” – you can use it as many times as you like within that video. Purchasing multiple licenses to support say repetition of a sound fx/audio file within an application wouldn’t make sense because that destroys the whole purpose of “loops” for instance.